/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date:        19. March 2015
* $Revision: 	V.1.4.5
*
* Project: 	    CMSIS DSP Library
* Title:		arm_correlate_fast_q31.c
*
* Description:	Fast Q31 Correlation.
*
* Target Processor: Cortex-M4/Cortex-M3
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in
*     the documentation and/or other materials provided with the
*     distribution.
*   - Neither the name of ARM LIMITED nor the names of its contributors
*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup Corr
 * @{
 */

/**
 * @brief Correlation of Q31 sequences (fast version) for Cortex-M3 and Cortex-M4.
 * @param[in] *pSrcA points to the first input sequence.
 * @param[in] srcALen length of the first input sequence.
 * @param[in] *pSrcB points to the second input sequence.
 * @param[in] srcBLen length of the second input sequence.
 * @param[out] *pDst points to the location where the output result is written.  Length 2 * max(srcALen, srcBLen) - 1.
 * @return none.
 *
 * @details
 * <b>Scaling and Overflow Behavior:</b>
 *
 * \par
 * This function is optimized for speed at the expense of fixed-point precision and overflow protection.
 * The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format.
 * These intermediate results are accumulated in a 32-bit register in 2.30 format.
 * Finally, the accumulator is saturated and converted to a 1.31 result.
 *
 * \par
 * The fast version has the same overflow behavior as the standard version but provides less precision since it discards the low 32 bits of each multiplication result.
 * In order to avoid overflows completely the input signals must be scaled down.
 * The input signals should be scaled down to avoid intermediate overflows.
 * Scale down one of the inputs by 1/min(srcALen, srcBLen)to avoid overflows since a
 * maximum of min(srcALen, srcBLen) number of additions is carried internally.
 *
 * \par
 * See <code>arm_correlate_q31()</code> for a slower implementation of this function which uses 64-bit accumulation to provide higher precision.
 */

void arm_correlate_fast_q31(
    q31_t *pSrcA,
    uint32_t srcALen,
    q31_t *pSrcB,
    uint32_t srcBLen,
    q31_t *pDst)
{
    q31_t *pIn1;                                   /* inputA pointer               */
    q31_t *pIn2;                                   /* inputB pointer               */
    q31_t *pOut = pDst;                            /* output pointer               */
    q31_t *px;                                     /* Intermediate inputA pointer  */
    q31_t *py;                                     /* Intermediate inputB pointer  */
    q31_t *pSrc1;                                  /* Intermediate pointers        */
    q31_t sum, acc0, acc1, acc2, acc3;             /* Accumulators                  */
    q31_t x0, x1, x2, x3, c0;                      /* temporary variables for holding input and coefficient values */
    uint32_t j, k = 0u, count, blkCnt, outBlockSize, blockSize1, blockSize2, blockSize3;  /* loop counter                 */
    int32_t inc = 1;                               /* Destination address modifier */


    /* The algorithm implementation is based on the lengths of the inputs. */
    /* srcB is always made to slide across srcA. */
    /* So srcBLen is always considered as shorter or equal to srcALen */
    if(srcALen >= srcBLen)
    {
        /* Initialization of inputA pointer */
        pIn1 = (pSrcA);

        /* Initialization of inputB pointer */
        pIn2 = (pSrcB);

        /* Number of output samples is calculated */
        outBlockSize = (2u * srcALen) - 1u;

        /* When srcALen > srcBLen, zero padding is done to srcB
         * to make their lengths equal.
         * Instead, (outBlockSize - (srcALen + srcBLen - 1))
         * number of output samples are made zero */
        j = outBlockSize - (srcALen + (srcBLen - 1u));

        /* Updating the pointer position to non zero value */
        pOut += j;

    }
    else
    {
        /* Initialization of inputA pointer */
        pIn1 = (pSrcB);

        /* Initialization of inputB pointer */
        pIn2 = (pSrcA);

        /* srcBLen is always considered as shorter or equal to srcALen */
        j = srcBLen;
        srcBLen = srcALen;
        srcALen = j;

        /* CORR(x, y) = Reverse order(CORR(y, x)) */
        /* Hence set the destination pointer to point to the last output sample */
        pOut = pDst + ((srcALen + srcBLen) - 2u);

        /* Destination address modifier is set to -1 */
        inc = -1;

    }

    /* The function is internally
     * divided into three parts according to the number of multiplications that has to be
     * taken place between inputA samples and inputB samples. In the first part of the
     * algorithm, the multiplications increase by one for every iteration.
     * In the second part of the algorithm, srcBLen number of multiplications are done.
     * In the third part of the algorithm, the multiplications decrease by one
     * for every iteration.*/
    /* The algorithm is implemented in three stages.
     * The loop counters of each stage is initiated here. */
    blockSize1 = srcBLen - 1u;
    blockSize2 = srcALen - (srcBLen - 1u);
    blockSize3 = blockSize1;

    /* --------------------------
     * Initializations of stage1
     * -------------------------*/

    /* sum = x[0] * y[srcBlen - 1]
     * sum = x[0] * y[srcBlen - 2] + x[1] * y[srcBlen - 1]
     * ....
     * sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen - 1] * y[srcBLen - 1]
     */

    /* In this stage the MAC operations are increased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = 1u;

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    pSrc1 = pIn2 + (srcBLen - 1u);
    py = pSrc1;

    /* ------------------------
     * Stage1 process
     * ----------------------*/

    /* The first stage starts here */
    while(blockSize1 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = count >> 2;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
            /* x[0] * y[srcBLen - 4] */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);
            /* x[1] * y[srcBLen - 3] */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);
            /* x[2] * y[srcBLen - 2] */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);
            /* x[3] * y[srcBLen - 1] */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);

            /* Decrement the loop counter */
            k--;
        }

        /* If the count is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = count % 0x4u;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            /* x[0] * y[srcBLen - 1] */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut = sum << 1;
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;

        /* Update the inputA and inputB pointers for next MAC calculation */
        py = pSrc1 - count;
        px = pIn1;

        /* Increment the MAC count */
        count++;

        /* Decrement the loop counter */
        blockSize1--;
    }

    /* --------------------------
     * Initializations of stage2
     * ------------------------*/

    /* sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen-1] * y[srcBLen-1]
     * sum = x[1] * y[0] + x[2] * y[1] +...+ x[srcBLen] * y[srcBLen-1]
     * ....
     * sum = x[srcALen-srcBLen-2] * y[0] + x[srcALen-srcBLen-1] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     */

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    py = pIn2;

    /* count is index by which the pointer pIn1 to be incremented */
    count = 0u;

    /* -------------------
     * Stage2 process
     * ------------------*/

    /* Stage2 depends on srcBLen as in this stage srcBLen number of MACS are performed.
     * So, to loop unroll over blockSize2,
     * srcBLen should be greater than or equal to 4 */
    if(srcBLen >= 4u)
    {
        /* Loop unroll over blockSize2, by 4 */
        blkCnt = blockSize2 >> 2u;

        while(blkCnt > 0u)
        {
            /* Set all accumulators to zero */
            acc0 = 0;
            acc1 = 0;
            acc2 = 0;
            acc3 = 0;

            /* read x[0], x[1], x[2] samples */
            x0 = *(px++);
            x1 = *(px++);
            x2 = *(px++);

            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            do
            {
                /* Read y[0] sample */
                c0 = *(py++);

                /* Read x[3] sample */
                x3 = *(px++);

                /* Perform the multiply-accumulate */
                /* acc0 +=  x[0] * y[0] */
                acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
                /* acc1 +=  x[1] * y[0] */
                acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
                /* acc2 +=  x[2] * y[0] */
                acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x2 * c0)) >> 32);
                /* acc3 +=  x[3] * y[0] */
                acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x3 * c0)) >> 32);

                /* Read y[1] sample */
                c0 = *(py++);

                /* Read x[4] sample */
                x0 = *(px++);

                /* Perform the multiply-accumulates */
                /* acc0 +=  x[1] * y[1] */
                acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x1 * c0)) >> 32);
                /* acc1 +=  x[2] * y[1] */
                acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x2 * c0)) >> 32);
                /* acc2 +=  x[3] * y[1] */
                acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x3 * c0)) >> 32);
                /* acc3 +=  x[4] * y[1] */
                acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x0 * c0)) >> 32);

                /* Read y[2] sample */
                c0 = *(py++);

                /* Read x[5] sample */
                x1 = *(px++);

                /* Perform the multiply-accumulates */
                /* acc0 +=  x[2] * y[2] */
                acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x2 * c0)) >> 32);
                /* acc1 +=  x[3] * y[2] */
                acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x3 * c0)) >> 32);
                /* acc2 +=  x[4] * y[2] */
                acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x0 * c0)) >> 32);
                /* acc3 +=  x[5] * y[2] */
                acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x1 * c0)) >> 32);

                /* Read y[3] sample */
                c0 = *(py++);

                /* Read x[6] sample */
                x2 = *(px++);

                /* Perform the multiply-accumulates */
                /* acc0 +=  x[3] * y[3] */
                acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x3 * c0)) >> 32);
                /* acc1 +=  x[4] * y[3] */
                acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x0 * c0)) >> 32);
                /* acc2 +=  x[5] * y[3] */
                acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x1 * c0)) >> 32);
                /* acc3 +=  x[6] * y[3] */
                acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x2 * c0)) >> 32);


            }
            while(--k);

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            while(k > 0u)
            {
                /* Read y[4] sample */
                c0 = *(py++);

                /* Read x[7] sample */
                x3 = *(px++);

                /* Perform the multiply-accumulates */
                /* acc0 +=  x[4] * y[4] */
                acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
                /* acc1 +=  x[5] * y[4] */
                acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
                /* acc2 +=  x[6] * y[4] */
                acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x2 * c0)) >> 32);
                /* acc3 +=  x[7] * y[4] */
                acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x3 * c0)) >> 32);

                /* Reuse the present samples for the next MAC */
                x0 = x1;
                x1 = x2;
                x2 = x3;

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut = (q31_t) (acc0 << 1);
            /* Destination pointer is updated according to the address modifier, inc */
            pOut += inc;

            *pOut = (q31_t) (acc1 << 1);
            pOut += inc;

            *pOut = (q31_t) (acc2 << 1);
            pOut += inc;

            *pOut = (q31_t) (acc3 << 1);
            pOut += inc;

            /* Increment the pointer pIn1 index, count by 4 */
            count += 4u;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pIn2;


            /* Decrement the loop counter */
            blkCnt--;
        }

        /* If the blockSize2 is not a multiple of 4, compute any remaining output samples here.
         ** No loop unrolling is used. */
        blkCnt = blockSize2 % 0x4u;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            while(k > 0u)
            {
                /* Perform the multiply-accumulates */
                sum = (q31_t) ((((q63_t) sum << 32) +
                                ((q63_t) * px++ * (*py++))) >> 32);
                sum = (q31_t) ((((q63_t) sum << 32) +
                                ((q63_t) * px++ * (*py++))) >> 32);
                sum = (q31_t) ((((q63_t) sum << 32) +
                                ((q63_t) * px++ * (*py++))) >> 32);
                sum = (q31_t) ((((q63_t) sum << 32) +
                                ((q63_t) * px++ * (*py++))) >> 32);

                /* Decrement the loop counter */
                k--;
            }

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            while(k > 0u)
            {
                /* Perform the multiply-accumulate */
                sum = (q31_t) ((((q63_t) sum << 32) +
                                ((q63_t) * px++ * (*py++))) >> 32);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut = sum << 1;
            /* Destination pointer is updated according to the address modifier, inc */
            pOut += inc;

            /* Increment the MAC count */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pIn2;


            /* Decrement the loop counter */
            blkCnt--;
        }
    }
    else
    {
        /* If the srcBLen is not a multiple of 4,
         * the blockSize2 loop cannot be unrolled by 4 */
        blkCnt = blockSize2;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* Loop over srcBLen */
            k = srcBLen;

            while(k > 0u)
            {
                /* Perform the multiply-accumulate */
                sum = (q31_t) ((((q63_t) sum << 32) +
                                ((q63_t) * px++ * (*py++))) >> 32);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut = sum << 1;
            /* Destination pointer is updated according to the address modifier, inc */
            pOut += inc;

            /* Increment the MAC count */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pIn2;

            /* Decrement the loop counter */
            blkCnt--;
        }
    }

    /* --------------------------
     * Initializations of stage3
     * -------------------------*/

    /* sum += x[srcALen-srcBLen+1] * y[0] + x[srcALen-srcBLen+2] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * sum += x[srcALen-srcBLen+2] * y[0] + x[srcALen-srcBLen+3] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * ....
     * sum +=  x[srcALen-2] * y[0] + x[srcALen-1] * y[1]
     * sum +=  x[srcALen-1] * y[0]
     */

    /* In this stage the MAC operations are decreased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = srcBLen - 1u;

    /* Working pointer of inputA */
    pSrc1 = ((pIn1 + srcALen) - srcBLen) + 1u;
    px = pSrc1;

    /* Working pointer of inputB */
    py = pIn2;

    /* -------------------
     * Stage3 process
     * ------------------*/

    while(blockSize3 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = count >> 2u;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            /* sum += x[srcALen - srcBLen + 4] * y[3] */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);
            /* sum += x[srcALen - srcBLen + 3] * y[2] */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);
            /* sum += x[srcALen - srcBLen + 2] * y[1] */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);
            /* sum += x[srcALen - srcBLen + 1] * y[0] */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);

            /* Decrement the loop counter */
            k--;
        }

        /* If the count is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = count % 0x4u;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            sum = (q31_t) ((((q63_t) sum << 32) +
                            ((q63_t) * px++ * (*py++))) >> 32);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut = sum << 1;
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;

        /* Update the inputA and inputB pointers for next MAC calculation */
        px = ++pSrc1;
        py = pIn2;

        /* Decrement the MAC count */
        count--;

        /* Decrement the loop counter */
        blockSize3--;
    }

}

/**
 * @} end of Corr group
 */
